Add test for 3D transform-origin support
Add test for 3D transform-origin support
Cross-platform `(-vendor-)transform-origin` support.

FF (19, at least) does not support the individual transform-origin properties (e.g, `transform-origin-x`, `transform-origin-y`). Neither prefixed nor otherwise.

Using the shorthand property gets around this limitation and, I think, could be faster because there are fewer operations.